A slight update to my JavaScript date extensions, DP_DateExtensions, is now available for download.  This release adds the ability to specify which day of week is considered the first day of the week when using the date math functions.  (Thanks to Neil Cresswell of cresswell.net for suggesting this addition.)

JavaScript itself considers Sunday (denoted as zero) the first day of the week by default.  This update provides access to a new property of the Date object, Date.FirstDayOfWeek, that can be set to any day from Sunday (zero) to Saturday (six).  This setting will then affect date math in the  round(), ceil(), floor() and diff() functions when the specified date part is “weeks”.

     // Set first day of week to Monday ("1")
Date.FirstDayOfWeek = 1
     // Create a new date
CurDate = new Date();
     // Perform some date math
RoundedWeek = CurDate.round("weeks");
FloorWeek = CurDate.floor("weeks")
CeilWeek = CurDate.ceil("weeks")

Personally I’ve not needed to leverage this yet, but I can definitely see it coming in handy.

A slight update to my JavaScript date extensions, DP_DateExtensions, is available for download.  This release addresses another issue related to paring of “AM” and “PM” indicators.  The gist of the problem was that the parser was transversing Noon and Midnight.

I had two bugs.  When I encountered a PM indicator I was simply adding 12 to the “hours” value if it were less than 13.  Of course 12 noon plus 12 hours is midnight the next day.  I needed to check for “less than 12” not “less than 13”.  However I also wasn’t taking any action if the indicator was AM – which left 12 AM as “12”, or noon, in the resulting 24 hour clock representation.  If the indicator were AM I needed to check if the hours were 12 and set them to zero if so.

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[Actually the “new” version is nearly a month old at this point but I forgot to do an entry to announce it.]

There’s a new version of my JavaScript date extensions, DP_DateExtensions, available.  This release fixes a significant, but interesting bug brought to my attention by Kevin Warnke.  He noticed that, sometimes, when you parsed a date with a 12-hour clock the resulting time was simply wrong – often off by weeks.  This, for some reason, annoyed him.

After digging I did find (and fix) the problem.  As you might expect to parse a time with a 12-hour time you need to take the time given and add 12 to it (if “PM”) to convert it to a 24-hour clock.  To do this I did some simple addition:

Hours = Hours + 12;

This worked fine in most cases.  However if “Hours” had leading zero, like “04” JavaScript treats this as a string and would result in “0412” rather than “16” as you might expect.  However when adding the value to a date JavaScript happily treats it as a number – so instead of adding 16 hours to my new date this resulted in adding 412 hours – or over 17 extra days!

Although there are many ways to fix this I decided to force the conversion by using the parseInt() function like so (the “10” indicates that you want to parse the value as base 10):

Hours = parseInt(Hours, 10) + 12;

This fixed the problem nicely.  In the end, a pretty silly error that I should have caught much sooner.